The present invention relates generally to the field of molecular biology and concerns a method for improving plant growth characteristics. More specifically, the present invention concerns a method for increasing yield and/or biomass of a plant by increasing the expression and/or activity of an LRR receptor kinase (RLK827) or a homologue thereof in a plant. The present invention also concerns plants having increased expression of a nucleic acid encoding an LRR receptor kinase or a homologue thereof, which plants have improved growth characteristics relative to corresponding wild type plants. The invention also provides constructs useful in the methods of the invention.
Given the ever-increasing world population, and the dwindling area of land available for agriculture, it remains a major goal of agricultural research to improve the efficiency of agriculture and to increase the diversity of plants in horticulture. Conventional means for crop and horticultural improvements utilise selective breeding techniques to identify plants having desirable characteristics. However, such selective breeding techniques have several drawbacks, namely that these techniques are typically labour intensive and result in plants that often contain heterogeneous genetic complements that may not always result in the desirable trait being passed on from parent plants. Advances in molecular biology have allowed mankind to manipulate the germplasm of animals and plants. Genetic engineering of plants entails the isolation and manipulation of genetic material (typically in the form of DNA or RNA) and the subsequent introduction of that genetic material into a plant. Such technology has led to the development of plants having various improved economic, agronomic or horticultural traits. Traits of particular economic interest are growth characteristics such as high yield. Yield is normally defined as the measurable produce of economic value from a crop. This may be defined in terms of quantity and/or quality. Yield is directly, dependent on several factors, for example, the number and size of the organs, plant architecture (for example, the number of branches), seed production and more. Root development, nutrient uptake and stress tolerance may also be important factors in determining yield. Crop yield may therefore be increased by optimising one of the abovementioned factors.
Growth and development of plants is determined by environmental and internal signals, such as hormone mediated signalling, stress and nutrient signalling, cell cycle control or developmental signalling. Cells perceive these signals via cell surface receptors, which transduce the signal to the inside of the cell. Many of these receptors are protein kinases. Protein kinases comprise a large family of enzymes that mediate the response of eukaryotic cells to stimuli by phosphorylation of hydroxyamino acids. The enzymes fall into two broad classes with respect to their substrate specificity: serine/threonine specific or tyrosine specific enzymes. Kinases involved in signal transduction may be classified into different families which are mostly made up of tyrosine kinases. Receptor Tyrosine Kinases (RTK) in animals have a uniform structure and are composed of an extracellular ligand binding domain, a transmembrane domain and a cytoplasmic tyrosine kinase domain. Among the plant tyrosine kinases, the Receptor-Like Kinase (RLK) proteins take a prominent place. More than 600 different RLKs are known in plants. They have a similar structure as the animal RTKs, a classification is given in FIG. 1 (Shiu and Bleecker, Proc. Natl. Acad. Sci. USA 98, 10763-10768, 2001). Several plant RLK proteins have been characterised, for example BRH (brassinoid signalling), CLV1 (meristem differentiation), HAESA (abscission of floral organs), XA21 (fungal detection) CR4 (leaf and endosperm development), FLS2 (flagellin/pathogen detection), SRK (self-incompatibility), among others (Becraft, Annu. Rev. Cell Dev. Biol. 18, 163-192, 2002; Dievart and Clark, Curr. Opin. Plant Biol. 6, 507-516). About 200 of the plant RLKs possess a Leucine Rich Repeat (LRR). LRRs are sequence motifs of 23 to 25 residues, which comprise a consensus sequence LxxLxLxxN/CxL wherein x may be any amino acid. These LRRs are present in proteins with diverse functions, such as hormone receptor interactions, enzyme inhibition, cell adhesion and cellular trafficking and frequently the LRR domains are organised in tandem arrays. It was shown that LRRs may be critical for the morphology and dynamics of the cytoskeleton. The primary function of these motifs appears to be providing a versatile structural framework for the formation of protein-protein interactions (Kobe and Kajava, Curr. Opin. Struct. Biol. 11, 725-732, 2001).
The combination of Leucine Rich Repeats and kinase domains is characteristic for receptor proteins that mediate external signals into the cell. They are thought to act by a mechanism in which the LRR domain(s), mostly extracellular, act as a sensor for an extracellular signal whereas the kinase domain is usually internal and participates in the transduction of the signal by phosphorylating intracellular targets and thus initiating the signal transduction. RLKs have been implicated in plants in a variety of process like plant development, disease resistance or self-incompatibility. It is shown in this invention that plant growth characteristics, and in particular yield, may be improved by modulating expression in a plant of a nucleic acid encoding an RLK.
International patent application WO 03/072763 disclosed a receptor like kinase which, when overexpressed in plants, resulted in increased plant growth and seed production. However, the subject RLK protein did not comprise any LRR domains in its non-cytoplasmic domain, but instead this domain was Proline rich. Another disclosure (WO 00/04761) reported that upon overexpression of the RKN receptor kinase, root growth was enhanced. Similarly, it was suggested, but not shown, in WO 98/59039 that overexpression of the BRH receptor kinase would result in modulated yield. However the RLK used in the latter two cases comprised 22 LRR domains in the non-cytoplasmic domain, typical for the LRR-X subfamily of receptor like kinases. So far there have been no reports to show or even suggest that receptor like kinases of the LRR-I subfamily may be useful for improving plant growth characteristics, and in particular in increasing yield.
It has now surprisingly been found that increasing expression and/or activity, relative to corresponding wild type plants, of an RLK827 protein in plants gives plants having improved growth characteristics, and in particular increased yield.
RLK827 is a receptor like kinase that is structurally related to LRRPK1 which is a member of the LRR-I subfamily of receptor like kinases (Shiu and Bleecker, 2001). The mature RLK827 protein has, starting from the N-terminus, a long putative non-cytoplasmic domain, a single transmembrane domain and a kinase domain in the C-terminal cytoplasmic part. The receptor like kinases are classified according to the composition of their non-cytoplasmic domain, which may comprise proline rich sequences, lectin domains, LRR domains, EGF repeats, TNFR repeats, thaumatin or agglutinin domains etc. A large group of receptor like kinases have Leucine Rich Repeats (LRR) in the non-cytoplasmic domain. The various LRR subfamilies differ from each other 0 in the number and position of these leucine rich repeats (for an overview, see Shiu and Bleecker, 2001). The putative non-cytoplasmic domain of RLK827 is characterised by the presence of one up to three tandem leucine rich repeat domains in its C-terminal part; RLK827 therefore belongs in the subfamily of LRR-I receptor kinases. The various LRR subfamilies of receptor kinases also differ from one other in their chromosomal distribution. Often they are arranged in tandem repeats. Tandem duplications, large-scale duplications and rearrangements of chromosomes are, at least in part, responsible for the evolution and expansion of the LRR receptor like kinases in plants. Accordingly, with a few exceptions, LRR-I receptor kinases are distributed on chromosome I, II and III in Arabidopsis. 
According to one embodiment of the present invention there is provided a method for improving growth characteristics of a plant comprising increasing expression and/or activity of an RLK827 polypeptide or a homologue thereof and optionally selecting for plants having improved growth characteristics.
Advantageously, performance of the methods according to the present invention result in plants having a variety of improved growth characteristics, such as improved growth, improved yield, improved biomass, modified architecture or improved cell division, each relative to corresponding wild type plants. Preferably, the improved growth characteristics comprise at least increased yield relative to corresponding wild type plants. Preferably, the increased yield is increased seed yield, which includes increased number of (filled) seeds, increased total weight of seeds and increased harvest index.
The term “increased yield” as defined herein is taken to mean an increase in any one or more of the following, each relative to corresponding wild type plants: (i) increased biomass (weight) of one or more parts of a plant, particularly aboveground (harvestable) parts, increased root biomass or increased biomass of any other harvestable part; (ii) increased total seed yield, which includes an increase in seed biomass (seed weight) and which may be an increase in the seed weight per plant (total seed weight) or on an individual seed basis; (iii) increased number of (filled) seeds; (iv) increased seed size; (v) increased seed volume; (vi) increased individual seed area; (vii) increased individual seed length; (viii) increased harvest index, which is expressed as a ratio of the yield of harvestable parts, such as seeds, over the total biomass; (ix) increased number of florets per panicle which is extrapolated from the total number of seeds counted and the number of primary panicles; and (x) increased thousand kernel weight (TKW), which is extrapolated from the number of filled seeds counted and their total weight. An increased TKW may result from an increased seed size (length, width or both) and/or seed weight. An increased TKW may result from an increase in embryo size and/or endosperm size.
Taking corn as an example, a yield increase may be manifested as one or more of the following: increase in the number of plants per hectare or acre, an increase in the number of ears per plant, an increase in the number of rows, number of kernels per row, kernel weight, TKW, ear length/diameter, among others. Taking rice as an example, a yield increase may be manifested by an increase in one or more of the following: number of plants per hectare or acre, number of panicles per plant, number of spikelets per panicle, number of flowers per panicle, increase in the seed filling rate, increase in TKW, among others. An increase in yield may also result in modified architecture, or may occur as a result of modified architecture.
Preferably, performance of the methods of the present invention results in plants having increased yield and/or increased biomass. More particularly, performance of the methods according to the present invention results in plants having increased seed yield. Preferably, the increased seed yield comprises an increase in one or more of number of filled seeds, total seed weight, and harvest index, each relative to control plants. Therefore, according to the present invention, there is provided a method for increasing plant yield, which method comprises increasing expression and/or activity in a plant of an RLK827 polypeptide or a homologue thereof.
Since the modified plants according to the present invention have increased yield, it is likely that these plants exhibit an increased growth rate (during at least part of their life cycle), relative to the growth rate of corresponding wild type plants at a corresponding stage in their life cycle. The increased growth rate may be specific to one or more parts or cell types of a plant (including seeds), or may be throughout substantially the whole plant. Plants having an increased growth rate may have a shorter life cycle. The life cycle of a plant may be taken to mean the time needed to grow from a dry mature seed up to the stage where the plant has produced dry mature seeds, similar to the starting material. This life cycle may be influenced by factors such as early vigour, growth rate, flowering time and speed of seed maturation. An increase in growth rate may take place at one or more stages in the life cycle of a plant or during substantially the whole plant life cycle. Increased growth rate during the early stages in the life cycle of a plant may reflect enhanced vigour. The increase in growth rate may alter the harvest cycle of a plant allowing plants to be sown later and/or harvested sooner than would otherwise be possible. If the growth rate is sufficiently increased, it may allow for the sowing of further seeds of the same plant species (for example sowing and harvesting of rice plants followed by sowing and harvesting of further rice plants all within one conventional growing period). Similarly, if the growth rate is sufficiently increased, it may allow for the sowing of further seeds of different plants species (for example the sowing and harvesting of rice plants followed by, for example, the sowing and optional harvesting of soy bean, potatoes or any other suitable plant). Harvesting additional times from the same rootstock in the case of some plants may also be possible. Altering the harvest cycle of a plant may lead to an increase in annual biomass production per acre (due to an increase in the number of times (say in a year) that any particular plant may be grown and harvested). An increase in growth rate may also allow for the cultivation of transgenic plants in a wider geographical area than their wild-type counterparts, since the territorial limitations for growing a crop are often determined by adverse environmental conditions either at the time of planting (early season) or at the time of harvesting (late season). Such adverse conditions may be avoided if the harvest cycle is shortened. The growth rate may be determined by deriving various parameters from growth curves plotting growth experiments, such parameters may be: T-Mid (the time taken for plants to reach 50% of their maximal size) and T-90 (time taken for plants to reach 90% of their maximal size), amongst others.
Performance of the methods of the invention gives plants having an increased growth rate. Therefore, according to the present invention, there is provided a method for increasing the growth rate of plants, which method comprises increasing expression and/or activity in a plant of an RLK827 polypeptide or a homologue thereof.
An increase in yield and/or growth rate occurs whether the plant is under non-stress conditions or whether the plant is exposed to various stresses compared to control plants. Plants typically respond to exposure to stress by growing more slowly. In conditions of severe stress, the plant may even stop growing altogether. Mild stress on the other hand is defined herein as being any stress to which a plant is exposed which does not result in the plant ceasing to grow altogether without the capacity to resume growth. Due to advances in agricultural practices (irrigation, fertilization, pesticide treatments) severe stresses are not often encountered in cultivated crop plants. As a consequence, the compromised growth induced by mild stress is often an undesirable feature for agriculture. Mild stresses are the typical stresses to which a plant may be exposed. These stresses may be the everyday biotic and/or abiotic (environmental) stresses to which a plant is exposed. Typical abiotic or environmental stresses include temperature stresses caused by atypical hot or cold/freezing temperatures; salt stress; water stress (drought or excess water). Abiotic stresses may also be caused by chemicals. Biotic stresses are typically those stresses caused by pathogens, such as bacteria, viruses, fungi and insects.
The abovementioned growth characteristics may advantageously be modified in any plant.
The term “plant” as used herein encompasses whole plants, ancestors and progeny of the plants and plant parts, including seeds, shoots, stems, leaves, roots (including tubers), flowers, and tissues and organs, wherein each of the aforementioned comprise the gene/nucleic acid of interest or the specific modification in the gene/nucleic acid of interest. The term “plant” also encompasses plant cells, suspension cultures, callus tissue, embryos, meristematic regions, gametophytes, sporophytes, pollen, and microspores, again wherein each of the aforementioned comprise the gene/nucleic acid of interest.
Plants that are particularly useful in the methods of the invention include algae, ferns, and all plants which belong to the superfamily Viridiplantae, in particular monocotyledonous and dicotyledonous plants, including fodder or forage legumes, ornamental plants, food crops, trees, or shrubs selected from the list comprising Abelmoschus spp., Acer spp., Actinidia spp., Agropyron spp., Allium spp., Amaranthus spp., Ananas comosus, Annona spp., Apium graveolens, Arabidopsis thaliana, Arachis spp, Artocarpus spp., Asparagus officinalis, Avena sativa, Averrhoa carambola, Benincasa hispida, Bertholletia excelsea, Beta vulgaris, Brassica spp., Cadaba farinosa, Camellia sinensis, Canna indica, Capsicum spp., Carica papaya, Carissa macrocarpa, Carthamus tinctorius, Carya spp., Castanea spp., Cichorium endivia, Cinnamomum spp., Citrullus lanatus, Citrus spp., Cocos spp., Coffea spp., Cola spp., Colocasia esculenta, Corylus spp., Crataegus spp., Cucumis spp., Cucurbita spp., Cynara spp., Daucus carota, Desmodium spp., Dimocarpus Iongan, Dioscorea spp., Diospyros spp., Echinochloa spp., Eleusine coracana, Eriobotrya japonica, Eugenia uniflora, Fagopyrom spp., Fagus spp., Ficus carica, Fortunella spp., Fragaria spp., Ginkgo biloba, Glycine spp., Gossypium hirsutum, Helianthus spp., Hibiscus spp., Hordeum spp., Ipomoea batatas, Juglans spp., Lactuca sativa, Lathyrus spp., Lemna spp., Lens culinaris, Linum usitatissimum, Litchi chinensis, Lotus spp., Luffa acutangula, Lupinus spp., Macrotyloma spp., Malpighia emarginata, Malus spp., Mammea americana, Mangifers indica, Manihot spp., Manilkara zapota, Medicago sativa, Melilotus spp., Mentha spp., Momordica spp., Morus nigra, Musa spp., Nicotiana spp., Olea spp., Opuntia spp., Ornithopus spp., Oryza spp., Panicum miliaceum, Passiflora edulis, Pastinaca sativa, Persea spp., Petroselinwn crispum, Phaseolus spp., Phoenix spp., Physalis spp., Pinus spp., Pistacia vera, Pisum spp., Poa spp., Populus spp., Prosopis spp., Prunus spp., Psidium spp., Punica granatum, Pyrus communis, Quercus spp., Raphanus sativus, Rheum rhabarbarum, Ribes spp., Rubus spp., Saccharum spp., Sambucus spp., Secale cereale, Sesamum spp., Solanum spp., Sorghum bicolor, Spinacia spp., Syzygium spp., Tamarindus indica, Theobroma cacao, Trifolium spp., Triticosecale rimpaui, Triticum spp., Vaccinium spp., Vicia spp., Vigna spp., Vitis spp., Zea mays, Zizania palustris, Ziziphus spp., amongst others.
According to a preferred feature of the present invention, the plant is a crop plant comprising soybean, sunflower, canola, alfalfa, rapeseed or cotton. Further preferably, the plant according to the present invention is a monocotyledonous plant such as sugarcane, most preferably a cereal, such as rice, maize, wheat, millet, barley, oats or sorghum.
The activity of an RLK827 protein may be increased by increasing levels of the RLK827 polypeptide. Alternatively, activity may also be increased when there is no change in levels of an RLK827, or even when there is a reduction in levels of an RLK827. This may occur when the intrinsic properties of the polypeptide are altered, for example, by making a mutant or selecting a variant that is more active that the wild type.
The term “RLK827 or homologue thereof” as defined herein refers to a Receptor Like Kinase (RLK) having kinase activity and comprising in its mature form a non-cytoplasmic domain (extracellular domain), a single transmembrane domain and a putative cytoplasmic kinase domain. The non-cytoplasmic domain or RLK827 comprises at least 1 but no more than 3 Leucine Rich Repeat (LRR) domains, preferably two LRR domains are present, more preferably three LRR domains. Further preferably, the length of the non-cytoplasmic domain ranges between 250 and 550 amino acids. The non-cytoplasmic domain preferably comprises the amino acid sequence motif LRxFP(E/D)GxRNC(Y/F) (SEQ ID NO: 33), wherein x may be any amino acid and where up to 2 other amino acids may be replaced by a conserved substitution as listed in Table 2. Preferably, the first x in this motif is Y or A, and the second x preferably is one of V, F, E and A.
The term “RLK827 or homologue thereof also refers to amino acid sequences having in increasing order of preference at least 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98% or 99% overall sequence identity to the amino acid represented by SEQ ID NO: 2.
The term “RLK827 or homologue thereof comprises RLK827 (SEQ ID NO 2), its paralogues and orthologues. The overall sequence identity is determined using a global alignment algorithm, such as the Needleman Wunsch algorithm in the program GAP (GCG Wisconsin Package, Accelrys), using default parameter settings.
The various structural domains in an RLK827 protein may be identified using specialised databases e.g. SMART (Schultz et al. (1998) Proc. Natl. Acad. Sci. USA 95, 5857-5864; Letunic et al. (2002) Nucleic Acids Res 30, 242-244; smart.embl-heidelberg.de webpage) or Pfam (Bateman et al., Nucleic Acids Research 30(1):276-280 (2002), sanger.ac.uk/Software/Pfam/webpage).
The kinase domain is of a STYKc type (SMART accession number SM00221, Interpro accession number IPRO04040) and has possibly dual-specificity Ser/Thr/Tyr kinase activity. In the N-terminal extremity of the catalytic domain there is a glycine-rich stretch of residues in the vicinity of a lysine residue, which has been shown to be involved in ATP binding. In the central part of the catalytic domain there is a conserved aspartic acid residue, which is important for the catalytic activity of the enzyme.
Furthermore, LRR domains are well known in the art and are defined in Pfam (accession PF00560) as 20 to 29-residue sequence motifs present in tandem arrays in a number of proteins with diverse functions, such as hormone receptor interactions, enzyme inhibition, cell adhesion and cellular trafficking. Recent studies revealed the involvement of LRR proteins in early mammalian development, neural development, cell polarization, regulation of gene expression and apoptosis signalling. The primary function of these motifs appears to be to provide a versatile structural framework for the formation of protein-protein interactions. Sequence analyses of LRR proteins suggested the existence of several different subfamilies of LRRs. Apparently the repeats from different subfamilies never occur simultaneously and most probably evolved independently. However, all major classes of LRR seem to have curved horseshoe structures with a parallel beta sheet on the concave side and mostly helical elements on the convex side. At least six families of LRR proteins, characterised by different lengths and consensus sequences of the repeats, have been identified. Eleven-residue segments of the LRRs (LxxLxLxxN/CxL), corresponding to the β-strand and adjacent loop regions, are usually conserved in LRR proteins, whereas the remaining parts of the repeats may be very different. Despite the differences, each of these variable parts contains two half-turns at both ends and a “linear” segment (as the chain follows a linear path overall), usually formed by a helix, in the middle. The concave face and the adjacent loops are the most common protein interaction surfaces on LRR proteins. 3D structures of some LRR protein-ligand complexes show that the concave surface of LRR domain is ideal for interaction with alpha-helices, thus supporting earlier conclusions that the elongated and curved LRR structure provides an outstanding framework for achieving diverse protein-protein interactions. Molecular modelling suggests that the pattern LxxLxL, which is often conserved and which is shorter than the previously proposed LxxLxLxxN/CxL, is sufficient to impart the characteristic horseshoe curvature to proteins with 20- to 30-residue repeats. LRR domains of an LRK827 protein may differ from the canonical LRR domains known in the art but may be identified by suitable computer algorithms, preferably those used in the Pfam database.
Transmembrane domains are about 15 to 30 amino acids long and are usually composed of hydrophobic residues that form an alpha helix. They are usually predicted on the basis of hydrophobicity (for example Klein et al., Biochim. Biophys. Acta 815, 468, 1985; or Sonnhammer et al., In J. Glasgow, T. Littlejohn, F. Major, R. Lathrop, D. Sankoff, and C. Sensen, editors, Proceedings of the Sixth International Conference on Intelligent Systems for Molecular Biology, pages 175-182, Menlo Park, Calif., 1998. AAAI Press.).
Methods for the search and identification of RLK827 homologues would be well within the realm of persons skilled in the art. Such methods comprise comparison of the sequences represented by SEQ ID NO 1 or 2, in a computer readable format, with sequences that are available in public databases such as MIPS (mips.gsf.de/webpage), GenBank (ncbi.nlm.nih.gov/Genbank/index.html webpage) or EMBL Nucleotide Sequence Database (ebi.ac.uk/embl/index.html webpage), using algorithms well known in the art for the alignment or comparison of sequences, such as GAP (Needleman and Wunsch, J. Mol. Biol. 48; 443-453 (1970)), BESTFIT (using the local homology algorithm of Smith and Waterman (Advances in Applied Mathematics 2; 482-489 (1981))), BLAST (Altschul, S. F., Gish, W., Miller, W., Myers, E. W. & Lipman, D. J., J. Mol. Biol. 215:403-410 (1990)), FASTA and TFASTA (W. R. Pearson and D. J. Lipman Proc.Natl.Acad.Sci. USA 85:2444-2448 (1988)). The software for performing BLAST analysis is publicly available through the National Centre for Biotechnology Information (NCBI). The homologues mentioned below were identified using BLAST default parameters (BLOSUM62 matrix, gap opening penalty 11 and gap extension penalty 1) and preferably the full-length sequences are used for analysis.
Examples of proteins falling under the definition of “RLK827 polypeptide or a homologue thereof” include the Arabidopsis proteins At1g51850, At1g51805, At1g51810, At2g04300, At3g21340, At1g49100. It should be noted that a cluster of related putative receptor like kinases are located in tandem on chromosome 1 of Arabidopsis thaliana, including At1g51800, At1g51805, At1g51810, At1g51820, At1g51830, At1g51840, At1g51850, At1g51860, At1g51870, At1g51880 and At1g51890, of which at least four of them are highly related to RLK827.
It is to be understood that the term RLK827 polypeptide or a homologue thereof is not to be limited to the sequences represented by SEQ ID NO: 2, SEQ ID NO: 7, SEQ ID NO: 11, SEQ ID NO: 13, SEQ ID NO: 15 or SEQ ID NO: 17 and SEQ ID NO: 19, but that any polypeptide meeting the criteria of (i) having a cytoplasmic kinase domain and (ii) having at least one but no more than three LRR domains and preferably the consensus sequence of SEQ ID NO: 33 in the putative non-cytoplasmic part of the protein, separated from the kinase domain by a transmembrane region, and which kinase domain comprises the STYKc consensus sequence and/or (iii) being a paralogue or orthologue of RLK827 and having at least 25% sequence identity to the sequence of SEQ ID NO: 2, may be suitable for use in the methods of the invention. Preferably, the kinase domain is functional, meaning that the RLK827 polypeptide or its homologue has kinase activity.
To determine the kinase activity of RLK827, several assays are available and well known in the art (for example Current Protocols in Molecular Biology, Volumes 1 and 2, Ausubel et al. (1994), Current Protocols; or online such as at the protocol-online org webpage). In brief, the kinase assay generally involves (1) bringing the kinase protein into contact with a substrate polypeptide containing the target site to be phosphorylated; (2) allowing phosphorylation of the target site in an appropriate kinase buffer under appropriate conditions; (3) separating phosphorylated products from non-phosphorylated substrate after a suitable reaction period. The presence or absence of kinase activity is determined by the presence or absence of a phosphorylated target. In addition, quantitative measurements can be performed. Purified RLK827 protein, or cell extracts containing or enriched in the RLK827 protein could be used as source for the kinase protein. Alternatively, the approach of Zhao et al. (Plant Mol. Biol. 26, 791-603, 1994) could be used, where the cytoplasmic domain of a rice receptor like kinase was expressed in Escherichia coli and assayed for kinase activity. As a substrate, small peptides are particularly well suited. The peptide must comprise one or more serine, threonine or tyrosine residues in a phosphorylation site motif. A compilation of phosphorylation sites can be found in Biochimica et Biophysica Acta 1314, 191-225, (1996). In addition, the peptide substrates may advantageously have a net positive charge to facilitate binding to phosphocellulose filters, (allowing to separate the phosphorylated from non-phosphorylated peptides and to detect the phosphorylated peptides). If a phosphorylation site motif is not known, a general tyrosine kinase substrate can be used. For example, “Src-related peptide” (RRLIEDAEYAARG) is a substrate for many receptor and non-receptor tyrosine kinases). To determine the kinetic parameters for phosphorylation of the synthetic peptide, a range of peptide concentrations is required. For initial reactions, a peptide concentration of 0.7-1.5 mM could be used. For each kinase enzyme, it is important to determine the optimal buffer, ionic strength, and pH for activity. A standard 5× Kinase Buffer generally contains 5 mg/ml BSA (Bovine Serum Albumin preventing kinase adsorption to the assay tube), 150 mM Tris-Cl (pH 7.5), 100 mM MgCl2. Divalent cations are required for most tyrosine kinases, although some tyrosine kinases (for example, insulin-, IGF-1-, and PDGF receptor kinases) require MnCl2 instead of MgCl2 (or in addition to MgCl2). The optimal concentrations of divalent cations must be determined empirically for each protein kinase. A commonly used donor for the phosphoryl group is radio-labelled [gamma-32P]ATP (normally at 0.2 mM final concentration). The amount of 32P incorporated in the peptides may be determined by measuring activity on the nitrocellulose dry pads in a scintillation counter.
Alternatively, the activity of an RLK827 polypeptide or of a homologue thereof may be assayed by expressing the RLK827 polypeptide or of a homologue thereof under control of a rice GOS2 promoter in rice plants, and in particular in the rice variety Nipponbare, which results in plants with increased yield compared to corresponding wild type plants. This increase in yield may for example be measured as one or more of an increase in number of filled seeds, in total weight of seeds and/or in harvest index.
The nucleic acid encoding an RLK827 polypeptide or a homologue thereof may be any natural or synthetic nucleic acid. An RLK827 polypeptide or a homologue thereof as defined herein is encoded by an RLK827 nucleic acid molecule. Therefore the term “RLK827 nucleic acid molecule” or “RLK827 gene” as defined herein is any nucleic acid molecule encoding an RLK827 polypeptide or a homologue thereof as defined above. Examples of RLK827 nucleic acid molecules include those represented by any one of SEQ ID NO: 1, SEQ ID NO: 6, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16 and SEQ ID NO: 18, SEQ ID NO 23, SEQ ID NO 25, SEQ ID NO 27, SEQ ID NO 29, SEQ ID NO 31. RLK827 nucleic acids and functional variants thereof may be suitable in practising the methods of the invention. Functional variant RLK827 nucleic acids include portions of an RLK827 nucleic acid molecule and/or nucleic acids capable of hybridising with an RLK827 nucleic acid molecule or with a nucleic acid molecule encoding a homologue of RLK827. The term “functional” in the context of a functional variant refers to a variant RLK827 nucleic acid molecule (i.e. a portion or a hybridising sequence), which encodes a polypeptide having kinase activity and comprising a non-cytoplasmic (extracellular) domain, which non-cytoplasmic domain comprises at least 1 but no more than 3 LRR motifs and preferably also the amino acid sequence motif of SEQ ID NO: 33 as defined above, and a C-terminal kinase domain, that is separated from the non-cytoplasmic domain by a transmembrane domain.
The LRR-I type of receptor like kinases in plants have a modular structure, and it has been shown that one LRR protein is able to bind different ligands, for example the tomato SR160 receptor and its tomato homologue tBRH are able to bind brassinolide hormones and systemin, a long distance signalling peptide. Brassinolide and systemin do not compete for binding, suggesting they bind to different sites. Therefore, it is envisaged that engineering of LRR domains (e.g. by altering the number of LRR domains, or by performing domain stacking (binding to same or different ligand(s)), or domain shuffling), in such a way that the activity of the LRR is retained or modified, is useful in generating variant RLK827 nucleic acid molecules for performing the methods of the invention. In a similar way, the kinase domain may be engineered to improve kinase activity. A preferred type of variant includes those generated by domain deletion, stacking or shuffling (see for example He et al., Science 288, 2360-2363, 2000, or U.S. Pat. Nos. 5,811,238 and 6,395,547).
The term portion as defined herein refers to a piece of DNA comprising at least 150 nucleotides. A portion may be prepared, for example, by making one or more deletions to an RLK827 nucleic acid. The portions may be used in isolated form or they may be fused to other coding (or non coding) sequences in order to, for example, produce a protein that combines several activities, one of them being protein kinase activity. When fused to other coding sequences, the resulting polypeptide produced upon translation could be bigger than that predicted for the RLK827 portion. The portion useful in the methods of the present invention comprises at least the kinase domain, preferably also a non-cytoplasmic LRR domain and a transmembrane domain located N-terminally of the kinase domain, more preferably the portion comprises in the non-cytoplasmic domain at least 1 but no more than 3 LRR domains, most preferably, the portion comprises in the non-cytoplasmic domain at least 1 but no more than 3 LRR domains and the amino acid sequence motif of SEQ ID NO: 33 as defined above. Preferably, the functional portion is a portion of a nucleic acid as represented by any one of SEQ ID NO: 1, SEQ ID NO: 6, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16 and SEQ ID NO: 18.
The term “hybridisation” as defined herein is a process wherein substantially homologous complementary nucleotide sequences anneal to each other. The hybridisation process can occur entirely in solution, i.e. both complementary nucleic acids are in solution. The hybridisation process can also occur with one of the complementary nucleic acids immobilised to a matrix such as magnetic beads, Sepharose beads or any other resin. The hybridisation process can furthermore occur with one of the complementary nucleic acids immobilised to a solid support such as a nitro-cellulose or nylon membrane or immobilised by e.g. photolithography to, for example, a siliceous glass support (the latter known as nucleic acid arrays or microarrays or as nucleic acid chips). In order to allow hybridisation to occur, the nucleic acid molecules are generally thermally or chemically denatured to melt a double strand into two single strands and/or to remove hairpins or other secondary structures from single stranded nucleic acids. The stringency of hybridisation is influenced by conditions such as temperature, salt concentration, ionic strength and hybridisation buffer composition.
“Stringent hybridisation conditions” and “stringent hybridisation wash conditions” in the context of nucleic acid hybridisation experiments such as Southern and Northern hybridisations are sequence dependent and may differ depending on environmental parameters. The skilled artisan is aware of various parameters which may be altered during hybridisation and washing and which will either maintain or change the stringency conditions.
The Tm is the temperature under defined ionic strength and pH, at which 50% of the target sequence hybridises to a perfectly matched probe. The Tm is dependent upon the solution conditions and the base composition and length of the probe. For example, longer sequences hybridise specifically at higher temperatures. The maximum rate of hybridisation is obtained from about 16° C. up to 32° C. below Tm. The presence of monovalent cations in the hybridisation solution reduce the electrostatic repulsion between the two nucleic acid strands thereby promoting hybrid formation; this effect is visible for sodium concentrations of up to 0.4M. Formamide reduces the melting temperature of DNA-DNA and DNA-RNA duplexes with 0.6 to 0.7° C. for each percent formamide, and addition of 50% formamide allows hybridisation to be performed at 30 to 45° C., though the rate of hybridisation will be lowered. Base pair mismatches reduce the hybridisation rate and the thermal stability of the duplexes. On average and for large probes, the Tm, decreases about 1° C. per % base mismatch. The Tm may be calculated using the following equations, depending on the types of hybrids:
DNA-DNA hybrids (Meinkoth and Wahl, Anal. Biochem., 138: 267-284, 1984):Tm=81.5° C.+16.6×log [Na+]a+0.41×%[G/Cb]−500×[Lc]−1−0.61×% formamideDNA-RNA or RNA-RNA hybrids:Tm=79.8+18.5(log10[Na+]a)+0.58 (% G/Cb)+11.8 (% G/Cb)2−820/Lc oligo-DNA or oligo-RNAd hybrids:
For <20 nucleotides: Tm=2 (/n)
For 20-35 nucleotides: Tm=22+1.46 (/n)    a or for other monovalent cation, but only accurate in the 0.01-0.4 M range.    b only accurate for % GC in the 30% to 75% range.    cL=length of duplex in base pairs.    d Oligo, oligonucleotide; /n, effective length of primer=2×(no. of G/C)+(no. of A/T).
Note: for each 1% formamide, the Tm is reduced by about 0.6 to 0.7° C., while the presence of 6M urea reduces the Tm by about 30° C.
Specificity of hybridisation is typically the function of post-hybridisation washes. To remove background resulting from non-specific hybridisation, samples are washed with dilute salt solutions. Critical factors of such washes include the ionic strength and temperature of the final wash solution: the lower the salt concentration and the higher the wash temperature, the higher the stringency of the wash. Wash conditions are typically performed at or below hybridisation stringency. Generally, suitable stringent conditions for nucleic acid hybridisation assays or gene amplification detection procedures are as set forth above. More or less stringent conditions may also be selected. Generally, low stringency conditions are selected to be about 50° C. lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. Medium stringency conditions are when the temperature is 20° C. below Tm, and high stringency conditions are when the temperature is 10° C. below Tm. For example, stringent conditions are those that are at least as stringent as, for example, conditions A-L; and reduced stringency conditions are at least as stringent as, for example, conditions M-R. Non-specific binding may be controlled using any one of a number of known techniques such as, for example, blocking the membrane with protein containing solutions, additions of heterologous RNA, DNA, and SDS to the hybridisation buffer, and treatment with Rnase.
Examples of hybridisation and wash conditions are listed in Table 1:
TABLE 1StringencyPolynucleotideHybrid LengthHybridization Temperature andWash TemperatureConditionHybrid±(bp)‡Buffer†and Buffer†ADNA:DNA> or65° C. 1×SSC; or 42° C., 1×SSC65° C.; 0.3×SSCequal to 50and 50% formamideBDNA:DNA<50Tb*; 1×SSCTb*; 1×SSCCDNA:RNA> or67° C. 1×SSC; or 45° C., 1×SSC67° C.; 0.3×SSCequal to 50and 50% formamideDDNA:RNA<50Td*; 1×SSCTd*; 1×SSCERNA:RNA> or70° C. 1×SSC; or 50° C., 1×SSC70° C.; 0.3×SSCequal to 50and 50% formamideFRNA:RNA<50Tf*; 1×SSCTf*; 1×SSCGDNA:DNA> or65° C. 4×SSC; or 45° C.,.4×SSC65° C.; 1×SSCequal to 50and 50% formamideHDNA:DNA<150Th*; 4×SSCTh*; 4×SSCIDNA:RNA> or67° C. 4×SSC; or 45° C., 4×SSC67° C.; 1×SSCequal to 50and 50% formamideJDNA:RNA<50Tj*; 4×SSCTj*; 4×SSCKRNA:RNA> or70° C. 4×SSC; or 40° C., 6×SSC67° C.; 1×SSCequal to 50and 50% formamideLRNA:RNA<50TI*; 2×SSCTI*; 2×SSCMDNA:DNA> or50° C. 4×SSC; or 40° C., 6×SSC50° C.; 2×SSCequal to 50and 50% formamideNDNA:DNA<50Tn*; 6×SSCTn*; 6×SSC0DNA:RNA> or55° C. 4×SSC; or 42° C., 6×SSC55° C.; 2×SSCequal to 50and 50% formamidePDNA:RNA<50Tp*; 6×SSCTp*; 6×SSCQRNA:RNA> or60° C. 4×SSC; or 45° C., 6×SSC60° C.; 2×SSCequal to 50and 50% formamideRRNA:RNA<50Tr*; 4×SSCTr*; 4×SSC‡The “hybrid length” is the anticipated length for the hybridising nucleic acid. When nucleic acids of known sequence are hybridised, the hybrid length may be determined by aligning the sequences and identifying the conserved regions described herein.†SSPE (1×SSPE is 0.15M NaCl, 1O mM NaH2PO4, and 1.25 mM EDTA, pH7.4) may be substituted for SSC (1×SSC is 0.15M NaCI and 15 mM sodium citrate) in the hybridisation and wash buffers; washes are performed for 15 minutes after hybridisation is complete. The hybridisations and washes may additionally include 5 × Denhardt's reagent, 0.5-1.0% SDS, 100 μg/ml denatured, fragmented salmon sperm DNA, 0.5% sodium pyrophosphate, and up to 50% formamide.*Tb-Tr: The hybridisation temperature for hybrids anticipated to be less than 50 base pairs in length should be 5-10° C. less than the melting temperature Tm of the hybrids; the Tm is determined according to the above-mentioned equations.±The present invention also encompasses the substitution of any one, or more DNA or RNA hybrid partners with either a PNA, or a modified nucleic acid.
For the purposes of defining the level of stringency, reference can conveniently be made to Sambrook et al. (2001) Molecular Cloning: a laboratory manual, 3rd Edition Cold Spring Harbor Laboratory Press, CSH, New York or to Current Protocols in Molecular Biology, John Wiley & Sons, N.Y. (1989).
For example, a nucleic acid encoding SEQ ID NO: 2 or a homologue thereof may be used in a hybridisation experiment. Alternatively fragments thereof may be used as probes. Depending on the starting pool of sequences from which the RLK is to be identified, different fragments for hybridization can be selected. For example, when a limited number of homologues with a high sequence identity to RLK827 are desired, a less conserved fragment may be used for hybridisation such as GGTAGACTCGCCAAAGAATTTGAACCACTCGTTGAT (nucleotides 184 to 219 of SEQ ID NO: 1). By aligning SEQ ID NO: 2 and homologues thereof it is possible to design equivalent nucleic acid fragments useful as probes for hybridisation. Preferably the hybridising sequence comprises at least the kinase domain, preferably also a non-cytoplasmic LRR domain and a transmembrane domain located N-terminally of the kinase domain, more preferably the portion comprises in the non-cytoplasmic domain at least 1 but no more than 3 LRR domains, most preferably, the portion comprises in the non-cytoplasmic domain at least 1 but no more than 3 LRR domains and the amino acid sequence motif of SEQ ID NO: 33 as defined above.
After hybridisation and washing, the duplexes may be detected by autoradiography (when radiolabeled probes were used) or by chemiluminescence, immunodetection, by fluorescent or chromogenic detection, depending on the type of probe labelling. Alternatively, a ribonuclease protection assay may be performed for detection of RNA:RNA hybrids
The RLK827 nucleic acid molecule or variant thereof may be derived from any natural or artificial source. The nucleic acid/gene or variant thereof may be isolated from a microbial source, such as bacteria, yeast or fungi, or from a plant, alga or animal (including human) source. This nucleic acid may be modified from its native form in composition and/or genomic environment through deliberate human manipulation. The nucleic acid is preferably of plant origin, whether from the same plant species (for example to the one in which it is to be introduced) or whether from a different plant species. The nucleic acid may be isolated from a dicotyledonous species, preferably from the family Brassicaceae, further preferably from Arabidopsis thaliana. More preferably, the RLK827 isolated from Arabidopsis thaliana is represented by SEQ ID NO: 1 and the RLK827 amino acid sequence is as represented by SEQ ID NO: 2.
Functional variants useful in the methods of the present invention also include alternative splice variants of an RLK827 nucleic acid molecule or gene. The term “alternative splice variant” as used herein encompasses variants of a nucleic acid sequence in which selected introns and/or exons have been excised, replaced or added. Such variants will be ones in which the biological activity of the protein is retained, which may be achieved by selectively retaining functional segments of the protein. Such splice variants may be found in nature or may be manmade. Methods for making such splice variants are well known in the art. Preferred splice variants are splice variants of a nucleic acid represented by SEQ ID NO: 1. Further preferred are splice variants encoding a polypeptide retaining kinase activity and having at least one but no more than three LRR domains in the putative non-cytoplasmic part of the protein, separated from the kinase domain by a transmembrane region. More preferred splice variants comprise in addition also the amino acid sequence motif of SEQ ID NO: 33 in the putative non-cytoplasmic domain. Most preferred splice variants of an RLK827 nucleic acid molecule are those that encode an RLK827 polypeptide as defined above.
Functional variants useful in the methods of the present invention furthermore include allelic variants of a nucleic acid encoding an RLK827 polypeptide or a homologue thereof, preferably an allelic variant of the nucleic acid represented by SEQ ID NO 1. Further preferably, the polypeptide encoded by the allelic variant has kinase activity and retains at least one but no more than three LRR domains in the putative non-cytoplasmic part of the protein, separated from the kinase domain by a transmembrane region. More preferred allelic variants comprise in addition also the amino acid sequence motif of SEQ ID NO: 33 in the putative non-cytoplasmic domain. Most preferred allelic variants of an RLK827 nucleic acid molecule are those that encode an RLK827 polypeptide as defined above. Allelic variants exist in nature and encompassed within the methods of the present invention is the use of these natural alleles. Allelic variants encompass Single Nucleotide Polymorphisms (SNPs), as well as Small Insertion/Deletion Polymorphisms (INDELs). The size of INDELs is usually less than 100 bp. SNPs and INDELs form the largest set of sequence variants in naturally occurring polymorphic strains of most organisms.
The expression and/or activity of an RLK827 polypeptide or a homologue thereof may also be increased by introducing a genetic modification (preferably in the locus of an RLK827 gene). The locus of a gene as defined herein is taken to mean a genomic region which includes the gene of interest and 10 kb up- or downstream of the coding region.
The genetic modification may be introduced, for example, by any one (or more) of the following methods: TDNA activation, TILLING, site-directed mutagenesis, homologous recombination, directed evolution or by introducing and expressing in a plant a nucleic acid encoding an RLK827 polypeptide or a homologue thereof. Following introduction of the genetic modification there follows a step of selecting for increased expression and/or activity of an RLK827 polypeptide, which increase in expression and/or activity gives plants having improved growth characteristics.
T-DNA activation tagging (Hayashi et al. Science 258, 1350-1353, 1992) involves insertion of T-DNA usually containing a promoter (may also be a translation enhancer or an intron), in the genomic region of the gene of interest or 10 KB up- or down stream of the coding region of a gene in a configuration such that such promoter directs expression of the targeted gene. Typically, regulation of expression of the targeted gene by its natural promoter is disrupted and the gene falls under the control of the newly introduced promoter. The promoter is typically embedded in a T-DNA. This T-DNA is randomly inserted into a plant genome, for example, through Agrobacterium infection and leads to overexpression of genes near to the inserted T-DNA. The resulting transgenic plants show dominant phenotypes due to overexpression of genes close to the introduced promoter. The promoter to be introduced may be any promoter capable of directing expression of a gene in the desired organism, in this case a plant. For example, constitutive, tissue-preferred, cell type-preferred and inducible promoters are all suitable for use in T-DNA activation.
A genetic modification may also be introduced in the locus of an RLK827 gene using the technique of TILLING (Targeted Induced Local Lesions IN Genomes). This is a mutagenesis technology useful to generate and/or identify, and to eventually isolate mutagenised variants of an RLK827 nucleic acid molecule capable of exhibiting RLK827 activity. TILLING also allows selection of plants carrying such mutant variants. These mutant variants may even exhibit higher RLK827 activity than that exhibited by the gene in its natural form. TILLING combines high-density mutagenesis with high-throughput screening methods. The steps typically followed in TILLING are: (a) EMS mutagenesis (Redei and Koncz (1992), In: C Koncz, N-H Chua, J Schell, eds, Methods in Arabidopsis Research. World Scientific, Singapore, pp 16-82; Feldmann et al., (1994) In: E M Meyerowitz, C R Somerville, eds, Arabidopsis. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., pp 137-172; Lightner and Caspar (1998), In: J Martinez-Zapater, J Salinas, eds, Methods on Molecular Biology, Vol. 82. Humana Press, Totowa, N.J., pp 91-104); (b) DNA preparation and pooling of individuals; (c) PCR amplification of a region of interest; (d) denaturation and annealing to allow formation of heteroduplexes; (e) DHPLC, where the presence of a heteroduplex in a pool is detected as an extra peak in the chromatogram; (f) identification of the mutant individual; and (g) sequencing of the mutant PCR product. Methods for TILLING are well known in the art (McCallum Nature Biotechnol. 18, 455-457, 2000, Stemple Nature Rev. Genet. 5, 145-150, 2004).
Site-directed mutagenesis may be used to generated variants of RLK827 nucleic acids or portions thereof that retain activity, namely, protein kinase activity. Several methods are available to achieve site-directed mutagenesis, the most common being PCR based methods (See for example Ausubel et al., Current Protocols in Molecular Biology. Wiley Eds., at the 4ulr.com/products/currentprotocols/index.html webpage).
Directed evolution may be used to generate variants of RLK827 nucleic acid molecules or portions thereof encoding RKS11 or RKS4 polypeptides or orthologues or portions thereof having an increased biological activity. Directed evolution consists of iterations of DNA shuffling followed by appropriate screening and/or selection (Castle et al., (2004) Science 304(5674): 1151-4; U.S. Pat. Nos. 5,811,238 and 6,395,547).
TDNA activation, TILLING, site-directed mutagenesis and directed evolution are examples of technologies that enable the generation novel alleles and variants of RLK827 that retain RLK827 function and which are therefore useful in the methods of the invention.
Homologous recombination allows introduction in a genome of a selected nucleic acid at a defined selected position. Homologous recombination is a standard technology used routinely in biological sciences for lower organism such as yeast or the moss Physcomitrella. Methods for performing homologous recombination in plants have been described not only for model plants (Offringa et al. (1990) EMBO J. 9, 3077-3084) but also for crop plants, for example rice (Terada et al., (2002) Nature Biotechnol. 20, 1030-1034; or lida and Terada (2004) Curr. Opin. Biotechnol. 15, 132-138). The nucleic acid to be targeted (which may be an RLK827 nucleic acid molecule or variant thereof as hereinbefore defined) need not be targeted to the locus of an RLK827 gene, but may be introduced in, for example, regions of high expression. The nucleic acid to be targeted may be an improved allele used to replace the endogenous gene or may be introduced in addition to the endogenous gene.
According to a preferred embodiment of the invention, plant growth characteristics may be improved by introducing and expressing in a plant a nucleic acid encoding an RLK827 polypeptide or a homologue thereof.
A preferred method for introducing a genetic modification (which in this case need not be in the locus of an RLK827 gene) is to introduce and express in a plant a nucleic acid encoding an RLK827 polypeptide or a homologue thereof. An RLK827 polypeptide or homologue thereof as mentioned above is one having kinase activity and comprising a non-cytoplasmic (extracellular) domain, which non-cytoplasmic domain comprises at least 1 but no more than 3 LRR motifs and preferably also the amino acid sequence motif of SEQ ID NO: 33 as defined above, and a C-terminal kinase domain that is separated from the non-cytoplasmic domain by a transmembrane domain. Preferably, the RLK827 polypeptide or homologue thereof has in increasing order of preference, at least 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% 96%, 97%, 98% or 99% overall sequence identity to the amino acid sequence represented by SEQ ID NO: 2.
“Homologues” of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes having amino acid substitutions, deletions and/or insertions relative to the unmodified protein in question and having similar biological and functional activity as the unmodified protein from which they are derived.
Encompassed by the term “homologues” are orthologous sequences and paralogous sequences, two special forms of homology which encompass evolutionary concepts used to describe ancestral relationships of genes.
The term “paralogous” relates to gene-duplications within the genome of a species leading to paralogous genes. Paralogues of RLK827 may easily be identified by performing a BLAST analysis against a set of sequences from the same species as the query sequence.
The term “orthologous” relates to homologous genes in different organisms due to speciation. Orthologues in, for example, monocot plant species may easily be found by performing a so-called reciprocal blast search. This may be done by a first blast involving blasting the sequence in question (for example, SEQ ID NO: 1 or SEQ ID NO: 2) against any sequence database, such as the publicly available NCBI database which may be found at: the ncbi.nlm.nih.gov webpage. If orthologues in rice were sought, the sequence in question would be blasted against, for example, the 28,469 full-length cDNA clones from Oryza sativa Nipponbare available at NCBI. BLASTn or tBLASTX may be used when starting from nucleotides or BLASTP or TBLASTN when starting from the protein, with standard default values. The blast results may be filtered. The full-length sequences of either the filtered results or the non-filtered results are then blasted back (second blast) against the sequences of the organism from which the sequence in question is derived. The results of the first and second blasts are then compared. An orthologue is found when the results of the second blast give as hits with the highest similarity an RLK827 nucleic acid or RLK827 polypeptide, for example, if one of the organisms is Arabidopsis thaliana then a paralogue is found. In the case of large families, ClustalW may be used, followed by the construction of a neighbour joining tree, to help visualize the clustering. Using a reciprocal BLAST procedure a rice orthologue (Unigene accession number Os.26918) was identified represented by the ESTs CB631540, CB628137.1 and CB31541.1. Preferred orthologues are those having the highest similarity to RLK827 or to a paralogue thereof in a reciprocal BLAST search. Other examples of rice orthologues are given in SEQ ID NOs 24, 26, 28, 30 and 32.
A homologue may be in the form of a “substitutional variant” of a protein, i.e. where at least one residue in an amino acid sequence has been removed and a different residue inserted in its place. Amino acid substitutions are typically of single residues, but may be clustered depending upon functional constraints placed upon the polypeptide; insertions will usually be of the order of about 1 to 10 amino acid residues. Preferably, amino acid substitutions comprise conservative amino acid substitutions (Table 2). To produce such homologues, amino acids of the protein may be replaced by other amino acids having similar properties (such as similar hydrophobicity, hydrophilicity, antigenicity, propensity to form or break α-helical structures or β-sheet structures). Conservative substitution tables are well known in the art (see for example Creighton (1984) Proteins. W.H. Freeman and Company).
TABLE 2Examples of conserved amino acid substitutions:ResidueConservative SubstitutionsAlaSerArgLysAsnGln; HisAspGluGlnAsnCysSerGluAspGlyProHisAsn; GlnIleLeu, ValLeuIle; ValLysArg; GlnMetLeu; IlePheMet; Leu; TyrSerThr; GlyThrSer; ValTrpTyrTyrTrp; PheValIle; Leu
Less conserved substitutions can be made in case the above-mentioned amino acid properties are not so critical.
A homologue may also be in the form of an “insertional variant” of a protein, i.e. where one or more amino acid residues are introduced into a predetermined site in a protein. Insertions may comprise amino-terminal and/or carboxy-terminal fusions as well as intra-sequence insertions of single or multiple amino acids. Generally, insertions within the amino acid sequence will be smaller than amino- or carboxy-terminal fusions, of the order of about 1 to 10 residues. Examples of amino- or carboxy-terminal fusion proteins or peptides include the binding domain or activation domain of a transcriptional activator as used in the yeast two-hybrid system, phage coat proteins, (histidine)6-tag, glutathione S-transferase-tag, protein A, maltose-binding protein, dihydrofolate reductase, Tag 100 epitope, c-myc epitope, FLAG®-epitope, lacZ, CMP (calmodulin-binding peptide), HA epitope, protein C epitope and VSV epitope.
Homologues in the form of “deletion variants” of a protein are characterised by the removal of one or more amino acids from a protein.
Amino acid variants of a protein may readily be made using peptide synthetic techniques well known in the art, such as solid phase peptide synthesis and the like, or by recombinant DNA manipulations. Methods for the manipulation of DNA sequences to produce substitution, insertion or deletion variants of a protein are well known in the art. For example, techniques for making mutations at predetermined sites in DNA are well known to those skilled in the art and include M 13 mutagenesis, T7-Gen in vitro mutagenesis (USB, Cleveland, Ohio), QuickChange Site Directed mutagenesis (Stratagene, San Diego, Calif.), PCR-mediated site-directed mutagenesis or other site-directed mutagenesis protocols.
The RLK827 polypeptide or homologue thereof may be a derivative. “Derivatives” include peptides, oligopeptides, polypeptides, proteins and enzymes which may comprise substitutions, deletions or additions of naturally and non-naturally occurring amino acid residues compared to the amino acid sequence of a naturally-occurring form of the protein, for example, as presented in SEQ ID NO 2. “Derivatives” of a protein encompass peptides, oligopeptides, polypeptides, proteins and enzymes which may comprise naturally occurring altered, glycosylated, acylated or non-naturally occurring amino acid residues compared to the amino acid sequence of a naturally-occurring form of the polypeptide. A derivative may also comprise one or more non-amino acid substituents compared to the amino acid sequence from which it is derived, for example a reporter molecule or other ligand, covalently or non-covalently bound to the amino acid sequence, such as a reporter molecule which is bound to facilitate its detection, and non-naturally occurring amino acid residues relative to the amino acid sequence of a naturally-occurring protein.
According to a preferred aspect of the present invention, enhanced or increased expression of an RLK827 nucleic acid molecule or variant thereof is envisaged. Methods for obtaining enhanced or increased expression of genes or gene products are well documented in the art and include, for example, overexpression driven by appropriate promoters, the use of transcription enhancers or translation enhancers. Isolated nucleic acids which serve as promoter or enhancer elements may be introduced in an appropriate position (typically upstream) of a non-heterologous form of a polynucleotide so as to upregulate expression of an RLK827 nucleic acid or variant thereof. For example, endogenous promoters may be, altered in vivo by mutation, deletion, and/or substitution (see, Kmiec, U.S. Pat. No. 5,565,350; Zarling et al., PCT/US93/03868), or isolated promoters may be introduced into a plant cell in the proper orientation and distance from a gene of the present invention so as to control the expression of the gene.
If polypeptide expression is desired, it is generally desirable to include a polyadenylation region at the 3′-end of a polynucleotide coding region. The polyadenylation region may be derived from the natural gene, from a variety of other plant genes, or from T-DNA. The 3′ end sequence to be added may be derived from, for example, the nopaline synthase or octopine synthase genes, or alternatively from another plant gene, or less preferably from any other eukaryotic gene.
An intron sequence may also be added to the 5′ untranslated region or the coding sequence of the partial coding sequence to increase the amount of the mature message that accumulates in the cytosol. Inclusion of a spliceable intron in the transcription unit in both plant and animal expression constructs has been shown to increase gene expression at both the mRNA and protein levels up to 1000-fold (Buchman and Berg, Mol. Cell. Biol. 8, 4395-4405 (1988); Callis et al., Genes Dev. 1, 1183-1200 (1987)). Such intron enhancement of gene expression is typically greatest when placed near the 5′ end of the transcription unit. Use of the maize introns Adh1-S intron 1, 2, and 6, the Bronze-1 intron are known in the art. See generally, The Maize Handbook, Chapter 116, Freeling and Walbot, Eds., Springer, N.Y. (1994).
The invention also provides genetic constructs and vectors to facilitate introduction and/or expression of the nucleotide sequences useful in the methods according to the invention.
Therefore, there is provided a gene construct comprising:                (i) an RLK827 nucleic acid molecule or functional variant thereof;        (ii) one or more control sequence capable of driving expression of the nucleic acid sequence of (i); and optionally        (iii) a transcription termination sequence.        
Constructs useful in the methods according to the present invention may be constructed using recombinant DNA technology well known to persons skilled in the art. The gene constructs may be inserted into vectors, which may be commercially available, suitable for transforming into plants and suitable for expression of the gene of interest in the transformed cells.
Plants are transformed with a vector comprising the sequence of interest (i.e., an RLK827 nucleic acid or functional variant thereof). The sequence of interest is operably linked to one or more control sequences (at least to a promoter). The terms “regulatory element”, “control sequence” and “promoter” are all used interchangeably herein and are to be taken in a broad context to refer to regulatory nucleic acid sequences capable of effecting expression of the sequences to which they are ligated. Encompassed by the aforementioned terms are transcriptional regulatory sequences derived from a classical eukaryotic genomic gene (including the TATA box which is required for accurate transcription initiation, with or without a CCAAT box sequence) and additional regulatory elements (i.e. upstream activating sequences, enhancers and silencers) which alter gene expression in response to developmental and/or external stimuli, or in a tissue-specific manner. Also included within the term is a transcriptional regulatory sequence of a classical prokaryotic gene, in which case it may include a −35 box sequence and/or −10 box transcriptional regulatory sequences. The term “regulatory element” also encompasses a synthetic fusion molecule or derivative which confers, activates or enhances expression of a nucleic acid molecule in a cell, tissue or organ. The term “operably linked” as used herein refers to a functional linkage between the promoter sequence and the gene of interest, such that the promoter sequence is able to initiate transcription of the gene of interest.
Advantageously, any type of promoter may be used to drive expression of the nucleic acid sequence. The promoter may be an inducible promoter, i.e. having induced or increased transcription initiation in response to a developmental, chemical, environmental or physical stimulus. An example of an inducible promoter being a stress-inducible promoter, i.e. a promoter activated when a plant is exposed to various stress conditions, is the water stress induced promoter WS118. Additionally or alternatively, the promoter may be a tissue-specific promoter, i.e. one that is capable of preferentially initiating transcription in certain tissues, such as the leaves, roots, seed tissue etc. An example of a seed-specific promoter is the rice oleosin 18 kDa promoter (Wu et al. (1998) J Biochem 123(3): 386-91).
Preferably, the RLK827 nucleic acid or functional variant thereof is operably linked to a constitutive promoter. A constitutive promoter is transcriptionally active during most, but not necessarily all, phases of its growth and development and is substantially ubiquitously expressed. Preferably, the constitutive promoter is a GOS2 promoter (from rice) (nucleotides 1 to 2193 in SEQ ID NO: 3). It should be clear that the applicability of the present invention is not restricted to the RLK827 nucleic acid represented by SEQ ID NO: 1, nor is the applicability of the invention restricted to expression of an RLK827 nucleic acid when driven by a GOS2 promoter. Examples of other constitutive promoters that may also be used to drive expression of a RLK827 nucleic acid are shown in Table 3 below.
TABLE 3Examples of constitutive promotersGene SourceExpression MotifReferenceActinConstitutiveMcElroy et al, Plant Cell, 2: 163-171, 1990CAMV 35SConstitutiveOdell et al, Nature, 313: 810-812,1985CaMV 19SConstitutiveNilsson et al., Physiol. Plant.100: 456-462, 1997GOS2Constitutivede Pater et al, Plant J Nov; 2(6): 837-44, 1992UbiquitinConstitutiveChristensen et al, Plant Mol. Biol.18: 675-689, 1992Rice cyclophilinConstitutiveBuchholz et al, Plant Mol Biol.25(5): 837-43, 1994Maize H3 histoneConstitutiveLepetit et al, Mol. Gen. Genet.231: 276-285, 1992Actin 2ConstitutiveAn et al, Plant J. 10(1); 107-121,1996
Optionally, one or more terminator sequences may also be used in the construct introduced into a plant. The term “terminator” encompasses a control sequence which is a DNA sequence at the end of a transcriptional unit which signals 3′ processing and polyadenylation of a primary transcript and termination of transcription. Additional regulatory elements may include transcriptional as well as translational enhancers. Those skilled in the art will be aware of terminator and enhancer sequences which may be suitable for use in performing the invention. Such sequences would be known or may readily be obtained by a person skilled in the art.
An example of an expression cassette comprising the RLK827 nucleic acid operably linked to the GOS2 promoter and further comprising a terminator sequence is given in SEQ ID NO: 3.
The genetic constructs of the invention may further include an origin of replication sequence, which is required for maintenance and/or replication in a specific cell type. One example is when a genetic construct is required to be maintained in a bacterial cell as an episomal genetic element (e.g. plasmid or cosmid molecule). Preferred origins of replication include, but are not limited to, the fl-ori and colE1.
The genetic construct may optionally comprise a selectable marker gene. As used herein, the term “selectable marker gene” includes any gene which confers a phenotype on a cell in which it is expressed to facilitate the identification and/or selection of cells which are transfected or transformed with a nucleic acid construct of the invention. Suitable markers may be selected from markers that confer antibiotic or herbicide resistance, that introduce a new metabolic trait or that allow visual selection. Examples of selectable marker genes include genes conferring resistance to antibiotics (such as nptII that phosphorylates neomycin and kanamycin, or hpt, phosphorylating hygromycin), to herbicides (for example bar which provides resistance to Basta; aroA or gox providing resistance against glyphosate), or genes that provide a metabolic trait (such as manA that allows plants to use mannose as sole carbon source). Visual marker genes result in the formation of colour (for example β-glucuranidase, GUS), luminescence (such as luciferase) or fluorescence (Green Fluorescent Protein, GFP, and derivatives thereof).
The present invention also encompasses plants obtainable by the methods according to the present invention. The present invention therefore provides plants obtainable by the methods according to the present invention, which plants have introduced therein an RLK827 nucleic acid or a functional variant thereof, or which plants have introduced therein a genetic modification, preferably in the locus of an RLK827 gene.
The invention also provides a method for the production of transgenic plants having improved growth characteristics, comprising introduction and expression in a plant of an RLK827 nucleic acid or a functional variant thereof.
More specifically, the present invention provides a method for the production of transgenic plants having improved growth characteristics, which method comprises:                (i) introducing into a plant or plant cell an RLK827 nucleic acid or a functional variant thereof; and        (ii) cultivating the plant cell under conditions promoting plant growth and development.        
The nucleic acid may: be introduced directly into a plant cell or into the plant itself (including introduction into a tissue, organ or any other part of a plant). According to a preferred feature of the present invention, the nucleic acid is preferably introduced into a plant by transformation.
The term “transformation” as referred to herein encompasses the transfer of an exogenous polynucleotide into a host cell, irrespective of the method used for transfer. Plant tissue capable of subsequent clonal propagation, whether by organogenesis or embryogenesis, may be transformed with a genetic construct of the present invention and a whole plant regenerated therefrom. The particular tissue chosen will vary depending on the clonal propagation systems available for, and best suited to, the particular species being transformed. Exemplary tissue targets include leaf disks, pollen, embryos, cotyledons, hypocotyls, megagametophytes, callus tissue, existing meristematic tissue (e.g., apical meristem, axillary buds, and root meristems), and induced meristem tissue (e.g., cotyledon meristem and hypocotyl meristem). The polynucleotide may be transiently or stably introduced into a host cell and may be maintained non-integrated, for example, as a plasmid. Alternatively, it may be integrated into the host genome. The resulting transformed plant cell may then be used to regenerate a transformed plant in a manner known to persons skilled in the art.
Transformation of plant species is now a fairly routine technique. Advantageously, any of several transformation methods may be used to introduce the gene of interest into a suitable ancestor cell. Transformation methods include the use of liposomes, electroporation, chemicals that increase free DNA uptake, injection of the DNA directly into the plant, particle gun bombardment, transformation using viruses or pollen and microprojection. Methods may be selected from the calcium/polyethylene glycol method for protoplasts (Krens et al. (1982) Nature 296, 72-74; Negrutiu et al. (1987) Plant Mol. Biol. 8, 363-373); electroporation of protoplasts (Shillito et al. (1985) Bio/Technol 3, 1099-1102); microinjection into plant material (Crossway et al. (1986) Mol. Gen. Genet. 202, 179-185); DNA or RNA-coated particle bombardment (Klein et al. (1987) Nature 327, 70) infection with (non-integrative) viruses and the like. Transgenic rice plants expressing an RLK827 gene are preferably produced via Agrobacterium-mediated transformation using any of the well known methods for rice transformation, such as described in any of the following: published European patent application EP 1198985 A1, Aldemita and Hodges (Planta 199, 612-617, 1996); Chan et al. (Plant Mol. Biol. 22, 491-506, 1993), Hiei et al. (Plant J. 6, 271-282, 1994), which disclosures are incorporated by reference herein as if fully set forth. In the case of corn transformation, the preferred method is as described in either lshida et al. (Nature Biotechnol. 14, 745-50, 1996) or Frame et al. (Plant Physiol. 129, 13-22, 2002), which disclosures are incorporated by reference herein as if fully set forth.
Generally after transformation, plant cells or cell groupings are selected for the presence of one or more markers which are encoded by plant-expressible genes co-transferred with the gene of interest, following which the transformed material is regenerated into a whole plant.
Following DNA transfer and regeneration, putatively transformed plants may be evaluated, for instance using Southern analysis, for the presence of the gene of interest, copy number and/or genomic organisation. Alternatively or additionally, expression levels of the newly introduced DNA may be monitored using Northern and/or Western analysis, both techniques being well known to persons having ordinary skill in the art. The cultivation of transformed plant cells into mature plants may thus encompass steps of selection and/or regeneration and/or growing to maturity.
The generated transformed plants may be propagated by a variety of means, such as by clonal propagation or classical breeding techniques. For example, a first generation (or T1) transformed plant may be selfed to give homozygous second generation (or T2) transformants, and the T2 plants further propagated through classical breeding techniques.
The generated transformed organisms may take a variety of forms. For example, they may be chimeras of transformed cells and non-transformed cells; clonal transformants (e.g., all cells transformed to contain the expression cassette); grafts of transformed and untransformed tissues (e.g., in plants, a transformed rootstock grafted to an untransformed scion).
The present invention clearly extends to any plant cell or plant produced by any of the methods described herein, and to all plant parts and propagules thereof. The present invention extends further to encompass the progeny of a primary transformed or transfected cell, tissue, organ or whole plant that has been produced by any of the aforementioned methods, the only requirement being that progeny exhibit the same genotypic and/or phenotypic characteristic(s) as those produced in the parent by the methods according to the invention. The invention also includes host cells containing an isolated RLK827 nucleic acid or a functional variant thereof. Preferred host cells according to the invention are plant cells. The invention also extends to harvestable parts of a plant according to the invention such as but not limited to seeds, leaves, fruits, flowers, stems, rhizomes, tubers and bulbs. The invention furthermore relates to products directly derived from a harvestable part of such a plant, such as dry pellets or powders, oil, fat and fatty acids, starch or proteins.
The present invention also encompasses the use of RLK827 nucleic acids or functional variants thereof and to the use of RLK827 polypeptides or homologues thereof.
One such use relates to improving the growth characteristics of plants. A preferred use relates to improving yield of plants, a more preferred use relates to increasing seed yield. The seed yield may include one or more of the following: increased number of (filled) seeds, increased seed weight, increased harvest index, among others.
RLK827 nucleic acids or functional variants thereof or RLK827 polypeptides or homologues thereof may find use in breeding programmes in which a DNA marker is identified which may be genetically linked to an RLK827 gene or variant thereof. The RLK827 or variants thereof or RLK827 or homologues thereof may be used to define a molecular marker. This DNA or protein marker may then be used in breeding programs to select plants having altered growth characteristics. The RLK827 gene or variant thereof may, for example, be a nucleic acid as represented by any one of SEQ ID NO: 1, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29 and SEQ ID NO: 31.
Allelic variants of an RLK827 may also find use in marker-assisted breeding programmes. Such breeding programmes sometimes require introduction of allelic variation by mutagenic treatment of the plants, using for example EMS mutagenesis; alternatively, the programme may start with a collection of allelic variants of so called “natural” origin caused unintentionally. Identification of allelic variants then takes place by, for example, PCR. This is followed by a selection step for selection of superior allelic variants of the sequence in question and which give rise improved growth characteristics in a plant. Selection is typically carried out by monitoring growth performance of plants containing different allelic variants of the sequence in question, for example, different allelic variants of any one of SEQ ID NO: 1, SEQ ID NO: 6, SEQ ID NO: 8, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 23, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29 and SEQ ID NO: 31. Growth performance may be monitored in a greenhouse or in the field. Further optional steps include crossing plants, in which the superior allelic variant was identified, with another plant. This could be used, for example, to make a combination of interesting phenotypic features.
An RLK827 nucleic acid or variant thereof may also be used as a probe for genetically and physically mapping the genes that they are a part of, and as markers for traits linked to those genes. Such information may be useful in plant breeding in order to develop lines with desired phenotypes. Such use of RLK827 nucleic acids or variants thereof requires only a nucleic acid sequence of at least 15 nucleotides in length. The RLK827 nucleic acids or variants thereof may be used as restriction fragment length polymorphism (RFLP) markers. Southern blots of restriction-digested plant genomic DNA may be probed with the RLK827 nucleic acids or variants thereof. The resulting banding patterns may then be subjected to genetic analyses using computer programs such as MapMaker (Lander et al. (1987) Genomics 1, 174-181) in order to construct a genetic map. In addition, the nucleic acids may be used to probe Southern blots containing restriction endonuclease-treated genomic DNAs of a set of individuals representing parent and progeny of a defined genetic cross. Segregation of the DNA polymorphisms is noted and used to calculate the position of the RLK827 nucleic acid or variant thereof in the genetic map previously obtained using this population (Botstein et al. (1980) Am. J. Hum. Genet. 32, 314-331).
The production and use of plant gene-derived probes for use in genetic mapping is described in Bematzky and Tanksley (Plant Mol. Biol. Reporter 4, 37-41, 1986). Numerous publications describe genetic mapping of specific cDNA clones using the methodology outlined above or variations thereof. For example, F2 intercross populations, backcross populations, randomly mated populations, near isogenic lines, and other sets of individuals may be used for mapping. Such methodologies are well known to those skilled in the art.
The nucleic acid probes may also be used for physical mapping (i.e., for the placing of sequences on physical maps; see Hoheisel et al. In: Nonmammalian Genomic Analysis: A Practical Guide, Academic press 1996, pp. 319-346, and references cited therein).
In another embodiment, the nucleic acid probes may be used in direct fluorescence in situ hybridization (FISH) mapping (Trask (1991) Trends Genet. 7, 149-154). Although current methods of FISH mapping favour use of large clones (several to several hundred KB; see Laan et al. (1995) Genome Res. 5, 13-20), improvements in sensitivity may allow performance of FISH mapping using shorter probes.
A variety of nucleic acid amplification-based methods of genetic and physical mapping may be earned out using the nucleic acids. Examples include allele-specific amplification (Kazazian (1989) J. Lab. Clin. Med. 11, 95-96), polymorphism of PCR-amplified fragments (CAPS; Sheffield et al. (1993) Genomics 16, 325-332), allele-specific ligation (Landegren et al. (1988) Science 241, 1077-1080), nucleotide extension reactions (Sokolov (1990) Nucleic Acid Res. 18, 3671), Radiation Hybrid Mapping (Walter et al. (1997) Nat. Genet. 7, 22-28) and Happy Mapping (Dear and Cook (1989) Nucleic Acid Res. 17, 6795-6807). For these methods, the sequence of a nucleic acid is used to design and produce primer pairs for use in the amplification reaction or in primer extension reactions. The design of such primers is well known to those skilled in the art. In methods employing PCR-based genetic mapping, it may be necessary to identify DNA sequence differences between the parents of the mapping cross in the region corresponding to the instant nucleic acid sequence. This, however, is generally not necessary for mapping methods.
In this way, generation, identification and/or isolation of modified plants with altered RLK827 expression and/or activity displaying improved growth characteristics can be performed.
RLK827 nucleic acids or functional variants thereof or RLK827 polypeptides or homologues thereof may also find use as growth regulators. Since these molecules have been shown to be useful in improving the growth characteristics of plants, they would also be useful growth regulators, such as herbicides or growth stimulators. The present invention therefore provides a composition comprising an RLK827 or a functional variant thereof or an RLK827 polypeptide or homologue thereof, together with a suitable carrier, diluent or excipient, for use as a growth regulator.
The methods according to the present invention result in plants having improved growth characteristics, as described hereinbefore. These advantageous growth characteristics may also be combined with other economically advantageous traits, such as further yield-enhancing traits, tolerance to various stresses, traits modifying various architectural features and/or biochemical and/or physiological features.